Embodiments of the present invention relate to gas turbine engine fuel nozzles and, more particularly, to aft heat shields at the aft ends of fuel nozzle tips.
Aircraft gas turbine engine staged combustion systems have been developed to limit the production of undesirable combustion product components such as oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO), particularly, in the vicinity of airports where they contribute to urban photochemical smog problems. Gas turbine engines also are designed to be fuel efficient and have a low cost of operation. Other factors that influence combustor design are the desires of users of gas turbine engines for efficient, low cost operation, which translates into a need for reduced fuel consumption while at the same time maintaining or even increasing engine output. As a consequence, important design criteria for aircraft gas turbine engine combustion systems include provisions for high combustion temperatures, in order to provide high thermal efficiency under a variety of engine operating conditions, as well as minimizing undesirable combustion conditions that contribute to the emission of particulates, and to the emission of undesirable gases, and to the emission of combustion products that are precursors to the formation of photochemical smog.
Effective intermixing of the injected fuel and the combustion air helps to minimize the production of the undesirable combustion product components. In that regard, numerous swirlers, mixer designs, and venturi designs have been proposed over the years to improve the mixing of the fuel and air. In this way, burning occurs uniformly over the entire mixture and reduces the level of HC and CO that result from incomplete combustion. Venturis promote better mixing of fuel and air in fuel nozzles which is useful in reducing undesirable combustion emissions. Venturis have been designed with aft heat shields at the aft end of the fuel nozzle to protect the venturi and the rest of the fuel nozzle tip from heat for reducing undesirable effects from thermal exposure. Heat shields have also been designed for use at the end of other conical wall sections in the fuel nozzle tip such as an annular pilot housing which supports a pilot nozzle in the fuel nozzle tip. An example of such a heat shield at the aft end of a conical section of an annular pilot housing is disclosed in U.S. Pat. No. 8,171,735 to Mancini, et al. which issued on May 8, 2012, entitled “Mixer Assembly For Gas Turbine Engine Combustor”, assigned to the assignee of this patent, and incorporated herein by reference.
Accordingly, it would be desirable to have a more effective heat shield to protect a venturi used for mixing fuel and air in fuel nozzles to protect the fuel nozzle tip from heat for reducing undesirable effects from thermal exposure. It is desirable to have venturis with integral heat shields having features that promote heat exchange and cooling of structures. It is highly desirable to provide better cooling of the aft heat shield in order to reduce effects of the high thermal loading on heat shield life. It is also desirable to provide a better design for replacing and welding in a new heat shield.